The Fe protein and the MoFe protein of nitrogenases from Rodospirillum rubrum, Bacillus polymyxa and Spirillum lipoferum are being purified so that their enzymatic and physical-chemical properties can be evaluated. A factor which activates the Fe protein of S. lipoferum is being isolated and purified; it will be characterized, and its mode of action will be studied. The physiology and biochemistry of the N2-fixing organism, S. lipoferum, is under investigation, and its ability to fix N2 in association with a variety of plants will be tested. Heterocysts will be isolated from heterocystous blue-green algae, and their respiratory and N2-fixing activity will be studied. Field investigations are being continued on the role of N2-fixing blue-green algae in the eutrophication of freshwater lakes.